Sodium is one of the most widely distributed Earth elements. Sodium weight accounts for approximately 2.83% (6th in rank) of the total weight of the Earth's crust. Sodium metal is active and has low melting point, high boiling point, and good thermal and electrical conductivities. This metal has a wide range of applications. Sodium cyanide, triphenylphosphine, sodium borohydride, sodium azide, sodium methylate, sodium ethoxide, sodium peroxide, sodium amide, sodium hydride, and other compounds are being commercially manufactured. They are used in metallurgy, pharmaceuticals, pesticides, printing, and dyeing. In the metallurgical industry, they are as a reducing agent in the preparation of titanium, zirconium, silicon, etc. Given its active chemical nature, sodium metal is difficult to purify.
Most purification methods of sodium currently use industrial sodium as raw material. Chemical, cold trap, distillation, and filtration methods are also used in the purification. However, the process and reaction times are considerably long. Vacuum distillation is a commonly used method to purify a low-melting point metal. The liquid saturation vapor pressure reduces under a negative pressure. Consequently, the boiling point also reduces, as well as the energy consumption. The liquid remains in a boiling state in vacuum distillation. Metal impurity is due to the strong convection inside the fluid, which is brought to the surface and forms fog particles that affect the purification. Recent research and applications of distillation-purification technology are about sub-boiling distillation. In addition, no technological innovation has used sub-boiling distillation to purify sodium metal.